Development of Close-Spaced Evaporation Technique for BaSi₂ Films toward Solar Cell Applications

BaSi2 has ideal optical properties for solar cell applications and can potentially realize solar cells with higher efficiency and lower cost than the mainstream crystalline Si solar cells. The close-spaced evaporation technique allows epitaxial growth of BaSi2 films on Si substrates with scalability to large areas. The technique itself and the properties of the BaSi2 films are reviewed in this article. Using a BaAl4–Ni source ground in a mortar and pestle, BaSi2 films with (001) preferred orientation are grown on Si(100) at 1000℃. Such a high temperature growth leads to film cracking. Mechanical activation of BaAl4–Ni by ball milling lowers the BaSi2 film formation temperature down to 700℃, resulting in crack-free films. The preferred orientation changes from (001) to (100). The crack-free BaSi2 films have low electron concentration around 1016 cm－3 and show clear photoconduction, suggesting potential availability for solar cells.